Explosive booster

ABSTRACT

An explosive booster for detonating insensitive blasting charges and a process for the manufacture thereof. The explosive booster has a core of detonating cord, the ends of which have been coated, encased in a sheath of relatively insensitive explosive material of high brisance.

United States Patent Dowling [451 Aug. 22, 1972 [54] EXPLOSIVE BOOSTER3,037,453 6/1962 Cook et a1. ..102/24 72 Inventor: Th P BowlingWhitehall Pa. 3,212,438 10/1965 Lawrence 102/24 [73] Assignee:Commercial Solvents Corporation Primary Examiner-Verlin R. Pendegrass[22] Filed: I Aug 10 1970 Attorney-Howard E. Post and Robert H. Dewey[21] Appl. No.1 62,676 ABSTRACT An explosive booster for detonatinginsensitive blasting charges and a process for the manufacture thereof.[22] 21.8.3] "102/2134; The explosive booster has a core of detonafingcord, nt. the ends of which have been coated encased in a Fleld ofSearch sheath f relatively insensitive exp osi e material of highbrisance. [56] References Cited 3 Claims, No Drawings UNITED STATESPATENTS 2,733,658 2/1956 Moat 102/24 EXPLOSIVE BOOSTER BACKGROUND OF THEINVENTION This invention relates to detonating means for relativelyinsensitive explosives and more particularly to boosters for insensitiveexplosives wherein reliable detonations are achieved through the use ofa detonating cord core having the ends of said cord coated with aspecific coating composition.

U.S. Pat. No. 3,359,902 to .l. J. Minnick et a1. and U.S. Pat. No.3,037,453, incorporated herein by reference, describe explosive boostershaving a core of detonating cord. Boosters of this type have beengenerally satisfactory in field use. However, some failures have beennoted, especially when the boosters have been used under conditionswherein the boosters have been subjected to relatively high waterpressures. The boosters of the present invention have been morereliable.

Accordingly, it is an object of the present invention to provide a newexplosive booster.

It is another object of the present invention to provide a process forthe manufacture of explosive boosters having high brisance and improvedresistance to water.

These and other objects and advantages of the invention will beunderstood from the description of the invention.

SUMMARY OF THE INVENTION The present invention provides an explosivedevice having a core of detonating cord substantially encased in asheath of relatively insensitive explosive material. In the explosivedevice the terminals of the detonating cord are coated with a coatingcontaining from about 60 percent to about 80 percent by weight of waxand from about percent to about 40 percent by weight of polyethylene.

In the process of manufacturing such boosters, the terminals are coatedwith the coating composition at a temperature of from about 220 to about240 F.

DETAILED DESCRIPTION OF THE INVENTION Explosive boosters, having highbrisance, for detonating relatively insensitive blasting charges, suchas oiled ammonium nitrate, have been widely used and are generally veryreliable. However, when explosive boosters having cores of detonatingcord, generally of the type described in the U.S. Pat. Nos. 3,359,902and 3,037,453, are used under conditions in which the booster issubjected to water pressure, some failures have been observed. Boostersare frequently subjected to relatively high water pressures whenshooting wet" holes.

Commercially available detonating cords, such as the widely usedPrimacord and E-cord, are substantially impervious to water. When loopsof detonating cord are used as the explosive core in explosive boosters,the core is, therefore, also substantially impervious to water exceptthat water can, of course, penetrate through the terminals. It was notbelieved that water penetration through the terminals of the detonatingcord would be a problem because the cord was normally totally encased ina sheath of explosive material of high brisance which was itselfsubstantially water impervious. However, it has been discovered thatduring the manufacture of such explosive boosters that the terminals ofthe detonating cord frequently appear near or at the surface of thesheath of explosive material. Also, some of the explosive boosters havebeen found to have cracks in the sheath thereof. Any of suchcircumstances would, therefore, enable water to penetrate the detonatingcord through the terminals thereof, and significant amounts of water inthe detonating cord frequently inactivates the detonating cord causingfailures of the explosive boosters.

It has now been discovered that the explosive boosters can be madesignificantly more reliable when the terminals are coated with asubstantially waterproof coating composition. Specifically the coatingcomposition contains from about 60 percent to about 80 percent by weightof wax and from about 20 percent to about 40 percent by weight ofpolyethylene. A coating composition of a substantially homogeneousmixture of percent wax and 30 percent polyethylene is specificallypreferred. Mixtures containing more than percent wax are usually toothin to produce an acceptable seal and they do not give the desiredwater resistance. Mixtures containing less than 60 percent wax aregenerally too viscous to permit easy application of the coating and,further, they have a tendency to block readily. By block is meant thatduring manufacture adjacent coated terminals tend to stick together.

The wax used in the coating composition is preferably a paraflin wax.Other natural and synthetic waxes may, however, be used. Thepolyethylene, of course, has a melting point below 220 F. andspecifically an emulsifier grade is used. Polyethylene used in coatingsis commercially available from many sources. The wax and polyethyleneare admixed into a substantially homogenous mixture at an elevatedtemperature before being applied to the terminals of the detonatingcord.

The coating composition is applied to the terminals of the detonatingcord in any suitable manner such as brush application, spraying, etc.,although dipping of the ends into the coating composition isspecifically preferred. The terminal is coated for at least one-fourthinch from the end and preferably at least one-half inch of the end ofthe detonating cord is coated. The coating composition is, of course, inmolten form and preferably is at a temperature within the range of fromabout 220 F. to about 240 F. with a temperature of about 230 F.producing good results. Temperatures below 220 F. causes excessiveblocking which results in large knobs of the coating composition at theend of the detonating cord. These knobs readily break off duringhandling, disturb the end seal thereby permitting the possible entranceof water into the detonating cord. Temperatures above 240 F. tend tocause the coating composition to attack the countering of the detonatingcord, specifically the countering of reinforced Primacord, and result ina softening of the countering sealant and an unravelling of thecountering fibers.

The following example, in the opinion of the inventor, represents thebest embodiment of the invention.

EXAMPLE A mixture of 70 percent paraffin wax and 30 percent polyethylenehaving a melting point of 200 F. is heated to a temperature of 230 F.and mixed to obtain a homogeneous molten mixture.

Twelve 24 inch lengths of reinforced Primacord detonating cord had theirterminals dipped to a depth of about 1 inch in the molten mixture tocoat the ends and were then formed into bow-ties and used in themanufacture of explosive boosters as illustrated in the J. J. Minni'cket al. US. Pat. No. 3,359,902. Torpex was used as the explosivesheathing material.

Explosive boosters were also made as above described in this exampleexcept that the terminals of the detonating cord were not coated.

Ten boosters having an explosive core of detonating cord of which theterminals were uncoated were subjected to water pressures of 80 p.s.i.for 16 hours and tested for sensitivity. When tested with a No. 6 cap inthe cap well, four out of ten boosters failed to detonate.

Twelve boosters, having an explosive core of detonating cord of whichthe terminals were coated in accordance with the present invention, weresubjected to water pressure of 80 p.s.i. for 16 hours and tested forsensitivity. When tested with a No. 1 cap in the cap well, 1 1 out ofthe 12 detonated completely.

I claim:

1. In an explosive device having a core of detonating cord substantiallyencased in a sheath of relatively insensitive explosive material theimprovement comprising a coating on the terminals of the detonatingcord, said coating containing from about 60 percent to about 80 percentby weight of wax and from about 20 percent to about 40 percent by weightof polyethylene.

2. In a process for manufacturing an explosive device having a core ofdetonating cord substantially surrounded by a sheath of less sensitiveexplosive material, the steps comprising coating the terminals of thedetonating cord with a sealing composition comprising from about 60percent to about 80 percent by weight of wax and from about 20 percentto about 40 percent by weight of polyethylene, said coating beingeffected at a temperature of from about 220 to about 240 F cooling thecoating and subsequently surrounding the terminaLcoated detonating cordwith a sheath of explosive material less sensitive than said detonatingcord.

3. The explosive device of claim 1 wherein said coating contains about70 percent by weight of paraffin wax and percent by weight of emulsifiergrade polyethylene.

1. In an explosive device having a core of detonating cord substantiallyencased in a sheath of relatively insensitive explosive material theimprovement comprising a coating on the terminals of the detonatingcord, said coating containing from about 60 percent to about 80 percentby weight of wax and from about 20 percent to about 40 percent by weightof polyethylene.
 2. In a process for manufacturing an explosive devicehaving a core of detonating cord substantially surrounded by a sheath ofless sensitive explosive material, the steps comprising coating theterminals of the detonating cord with a sealing composition comprisingfrom about 60 percent to about 80 percent by weight of wax and fromabout 20 percent to about 40 percent by weight of polyethylene, saidcoating being effected at a temperature of from about 220* to about 240*F., cooling the coating and subsequently surrounding the terminal-coateddetonating cord with a sheath of explosive material less sensitive thansaid detonating cord.
 3. The explosive device of claim 1 wherein saidcoating contains about 70 percent by weight of paraffin wax and 30percent by weight of emulsifier grade polyethylene.